I didn't need to change anything on the 870 and it worked, but the not consistently. The 870 loses internet access often. Sometimes it gets it back, and sometimes I need to power-cycle it.

Given how well it worked before, is there some firewall / port setting I no longer remember that I need to take care of? I'm happy to read a manual if one is available, but the Cisco documents I've seen so far don't discuss this topology, and I can't connect the 870 to the cable modem or wire it directly to the router.